The Stellar Spectra Factory(SSF)Based on SLAM

An empirical stellar spectral library with large coverage of stellar parameters is essential for stellar population synthesis and studies of stellar evolution.In this work,we present Stellar Spectra Factory(SSF),a tool to generate empirical-based stellar spectra from arbitrary stellar atmospheric parameters.The relative flux-calibrated empirical spectra can be predicted by SSF given arbitrary effective temperature,surface gravity,and metallicity.SSF constructs the interpolation approach based on the Stellar LAbel Machine,using ATLAS-A library,which contains spectra covering from O type to M type,as the training data set.SSF is composed of four data-driven sub-models to predict empirical stellar spectra.Sub-model SSF-N can generate spectra from A to K type and some M giant stars,covering 3700<T_(eff)<8700 K,0<logg<dex,and-1.5<[M/H]<0.5 dex.Sub-model SSF-gM is mainly used to predict M giant spectra with 3520<T_(eff)<4000 K and-1.5<[M/H]<0.4 dex.Sub-model SSF-dM is for generating M dwarf spectra with 3295<T_(eff)<4040 K,-1.0<[M/H]<0.1 dex.Sub-model SSF-B can predict B-type spectra with 9000<T_(eff)<24,000 K and-5.2<M_(G)<1.5 mag.The accuracy of the predicted spectra is validated by comparing the flux of predicted spectra to those with same stellar parameters selected from the known spectral libraries,MILES and MaStar.The averaged difference of flux over optical wavelength between the predicted spectra and the corresponding ones in MILES and MaStar is less than 5%.More verification is conducted between the magnitudes calculated from the integration of the predicted spectra and the observations in PS1 and APASS bands with the same stellar parameters.No significant systematic difference is found between the predicted spectra and the photometric observations.The uncertainty is 0.08 mag in the r band for SSF-gM when comparing with the stars with the same stellar parameters selected from PS1.The uncertainty becomes 0.31 mag in the i band for SSF-dM when comparing with the stars with the same stellar parameters selected from APASS.

Spectroscopic Determination of C,N,and O Abundances of Solar-analog Stars Based on the Lines of Hydride Molecules

Photospheric C,N,and O abundances of 118 solar-analog stars were determined by applying the synthetic-fitting analysis to their spectra in the blue or near-UV region comprising lines of CH,NH,and OH molecules,with an aim of clarifying the behaviors of these abundances in comparison with[Fe/H].It turned out that,in the range of-0.6■[Fe/H]■+0.3,[C/Fe]shows a marginally increasing tendency with decreasing[Fe/H]with a slight upturn around[Fe/H]~0,[N/Fe]tends to somewhat decrease toward lower[Fe/H],and[O/Fe]systematically increases (and thus[C/O]decreases) with a decrease in[Fe/H].While these results are qualitatively consistent with previous determinations mostly based on atomic lines,the distribution centers of these[C/Fe],[N/Fe],and[O/Fe]at the near-solar metallicity are slightly negative by several hundredths of dex,which is interpreted as due to unusual solar abundances possibly related to the planetary formation of our solar system.However,clear anomalies are not observed in the[C,N,O/Fe]ratios of planet-host stars.Three out of four very Be-deficient stars were found to show anomalous[C/Fe]or[N/Fe]which may be due to mass transfer from the evolved companion,though its relation to the Be depletion mechanism is still unclear.

Abundance analysis of Barium stars

We obtain the chemical abundances of six barium stars and two CH subgiant stars based on the high signal-to-noise ratio and high resolution EcheUe spectra. The neu-Iron capture process elements Y, Zr, Ba, La and Eu show obvious overabundances relative to the Sun, for example, their [Ba/Fe] values are from 0.45 to 1.27. Other elements, including Na, Mg, A1, Si, Ca, Sc, Ti, V, Cr, Mn and Ni, show comparable abundances to the Solar ones, and their [Fe/H] covers a range from -0.40 to 0.21, which means they belong to the Galactic disk. The predictions of the theoretical model of wind accretion for binary systems can explain the observed abundance patterns of the neutron capture process elements in these stars, which means that their overabundant heavy-elements could be caused by accreting the ejecta of AGB stars, the progenitors of present-day white dwarf companions in binary systems.

Non-LTE Analysis of the Sodium Abundance of Metal- Poor Stars in the Galactic Disk and Halo

We performed an extensive non-LTE analysis of the neutral sodium lines of Na I 5683/5688, 5890/5896, 6154/6161, and 8183/8195 in disk/halo stars of types F-K covering a wide metallicity range (-4 (?) [Fe/H] (?) +0.4), using our own data as well as data collected from the literature. For comparatively metal-rich disk stars (-1(?) [Fe/H] (?) +0.4) where the weaker 6154/6161 lines are the best abundance indicators, we confirmed [Na/Fe]- 0 with an 'upturn' (i.e., a shallow/broad dip around -0.5 (?) [Fe/H](?) 0) as already reported in previous studies. For the metal-deficient halo stars, where the much stronger 5890/5896 or 8183/8195 lines subject to considerable (negative) non-LTE corrections amounting to 0.5 dex have to be used, our analysis suggests mildly 'subsolar' [Na/Fe] values down to--0.4 (with a somewhat large scatter of-±0.2 dex) on the average at the typical halo metallicity of [Fe/H] --2, followed by a rise again to a near-solar ratio of [Na/Fe] - 0 at the very metal-poor regime [Fe/H]--3 to -4. These results are discussed in comparison with the previous observational studies along with the theoretical predictions from the available chemical evolution models.